The present invention relates to a liquid cooling system, and, in particular, to a liquid cooling system that is suitable for use in an ultra-small and/or thin electronic device.
Semiconductor devices, that are used in electronic devices, such as a computer, etc., generate heat during their operation. In particular, high-integrated semiconductor devices, in recent years, have produced an increased amount of heat generation. Since the semiconductor devices will be damaged and incapable of functioning if the temperature thereof exceeds a certain value, cooling is necessary to prevent damage to semiconductor devices having a large amount of heat generation during use.
For cooling the semiconductor devices of an electronic apparatus, there are various known techniques, such as thermal conduction or air-cooling, or the use of a heat pipe, or liquid cooling.
Cooling by thermal conduction is achieved by using materials having a large thermal conductivity along the heat radiating route, extending from the semiconductor device to the outside of the electronic apparatus. This method has been suitable for a so-called compact electronic apparatus, in which eat generation is relatively small, such as a notebook-type personal computer.
With cooling by the use of forced air, an air blower or fan is provided inside the electronic apparatus, thereby achieving a cooling of the semiconductor device therein by forced circulation of air thereon. This method is adopted widely for the cooling of semiconductor devices having a higher amount of heat generation, and it also has been applied to a personal computer by making the air blower small and thin in size.
Cooling with the use of a heat pipe involves carrying heat out to the outside of the electronic apparatus by means of coolant enclosed within a pipe, as described in Japanese Patent Laying-Open NO. Hei 1-184699 (1989), and Japanese Patent Laying-Open No. Hei 2-244748 (1989), for example. With this method, since there is no part capable of consuming electric power therein, such as an air blower or fan, such a cooling device has good efficiency, i.e., it increases the cooling through thermal conduction. However, with this method, there is a limit to the amount of heat that can be transferred.
Cooling by means of a liquid coolant is suitable for the cooling of a semiconductor device which generates a large amount of heat, and such a cooling device is described, for example, in Japanese Patent Laying-Open No. Hei 5-1335454 (1993), Japanese Patent Laying-Open No. Hei 6-97338 (1994), Japanese Patent Laying-Open No. Hei 6-125188 (1994), and Japanese Patent Laying-Open No. Hei 10-2 13370 (1998). However, such a cooling system using a liquid coolant has been restricted as to its field of utilization, such as to a large-scale computer. This is because the cooling system using a liquid coolant requires a large number of parts, such as a pump, a pipe system, heat radiation fins, etc., which are used exclusively for cooling, and so the apparatus comes to be large in size. Thus, it is difficult to maintain a satisfactory reliability when using liquid for cooling compared to other methods. It is also one reason why, on the commercial market, no semiconductor device requiring such a high level of cooling employs a liquid coolant system, other than in the field of the large-scale computers.
A technique for adapting the liquid cooling to a small-sized apparatus, including a notebook-sized personal computer, is described in Japanese Patent Laying-Open No. Hei 6-266474 (1994). In this cooling device, a header attached onto the semiconductor device and a heat radiation pipe separately located from it are connected with each other by means of a flexible tube to form a cooling system, and cooling is obtained by causing liquid coolant to flow therethrough.
However, there has been a remarkable increase in the heat generation produced from semiconductor devices which are used in electronic devices, such as a personal computer, a server computer, a work station, etc., in recent years. In addition, there has been a demand for electronic devices, such as a notebook-type personal computer, to be ultra-small and thin in size as well. For cooling the semiconductor devices used in those devices, various cooling methods have been adopted, such as thermal conduction, air-cooling, and/or the use of a heat pipe, as mentioned previously, however, the capacity of such cooling is still insufficient.
Also, for applying a liquid cooling system, which has been conventionally used in a large-scaled computer, to those electronic devices that are ultra-small and thin in size, it is a necessary condition that the liquid cooling system itself be ultra-small and thin in size. With such a system, the amount of liquid coolant retained therein is remarkably small, such as about {fraction (1/10,000)}. Because of the small amount of liquid coolant, the quality of the liquid coolant is easily lowered or degraded, even with a very small amount of elusion of corrosive ions from material that is in contact with the liquid coolant, which promotes corrosion in the heat receiving jacket and/or the heat radiation pipe, both of which are typically made of metal. Since leakage of the liquid coolant undesirably affects the function of the apparatus, this leakage must be suppressed, however, measures taken to avoid this problem have been insufficient, according to conventional techniques.